Blasting is one of the main means of minerals extraction in mining operations. The main purpose of the blasting operation is the rock fragmentation and this requires a large amount of explosives. Explosives release a large amount of energy during the explosion, where only 20-30% is used for rock breakage and displacement, while the rest of this energy is wasted in the environment.
Blasting can be defined as the ignition of an explosives massive charge. The blasting process includes loading the drills made in the bore with an explosive substance, which upon activation causes a shockwave and by means of a reaction, releases gases at high pressure and temperature of an instantaneous form for tearing, fracturing or removing a quantity of material according to the design parameters of the blasting.
The fragmentation of the rocky massif is caused immediately after the detonation. The impact effect of the shockwave and rapidly expanding gases on the drill wall is transferred to the surrounding rock, diffusing through it in the form of waves or forces of compression, causing only elastic deformation, since the rocks are very resistant to compression. When these waves reach the free face in the blasting front they cause tensile stresses on the rock mass between the free face and the drill. If the tensile strength of the rock is exceeded, it breaks in the area of the line of least resistance (burden). In this case, the reflected waves are voltage waves that return to the point of origin creating clefts and cracks of tension from the existing natural weakness planes and points, cracking it deeply (crackled effect).
Almost simultaneously, the volume of released and expanding gases penetrates into the initial cracks by expanding them by wedge action and creating new ones, with which effective rock fragmentation occurs. If the distance between the drill and the free face is correctly calculated, the rock between the two points will yield. Then the remnant gases rapidly move the mass of crushed material forward until it loses its force by cooling and by increasing the volume of the cavity formed in the rock. At this point, the fragments or debris fall and accumulate to form the pile of debris or blasted material.
In order to increase the performance and advance of the detonation fronts in the mine, explosive mixtures with higher energy technical characteristics, higher detonation velocity (resulting in greater detonation pressure and greater brisance or breaking power), resistant to water and greater volume of gases are required. The explosive mixture of the embodiments of the present invention is precisely characterized by having greater energy, greater volume of gases, and sensitivity to the No. 8 detonator and an excellent resistance to water, and since it doesn't contain nitroglycerin presents a better security in its handling and storage.
In the prior art, there are currently explosive mixtures comprising a mixture based on water-in-oil emulsion and ammonium nitrate granules (prills) of technical grade and/or anfo grade. The granules may be coated with petroleum and/or mineral oils. These explosive mixtures may be pumpable or packaged in plastic sleeves or in bags with diameters greater than 2½ inches (6.35 cm), they are not sensitive to No. 8 detonator but to a ⅓ pound (0.73 kg) booster for initiation as column loading.
In general, explosive mixtures of water-in-oil emulsion and granules (prills) of fertilizer-grade ammonium nitrate have the technical advantage with respect to emulsions and dynamites to present higher energy, higher bulk density and higher volume of gases which allows for better rock fragmentation. The problem of explosive mixtures of ammonium nitrate prills with technical grade and/or anfo grade lies in the instability of the explosive mixture due to the hygroscopicity of the ammonium nitrate which tends to adsorb the water found in the dispersed phase of the emulsion and the deterioration of the continuous phase of the emulsion by the action of the anticaking additives of ammonium nitrate based on sodium naphthalene sulfonate (Galoryl), resulting in a decrease in its life time, b) insensitivity to detonator No. #8, c) non-operation in cartridges of ⅞″ (0.34 cm) diameter (critical diameter), d) hardening of cartridges, which makes priming difficult and e) decrease in their explosive properties.
In this sense, the Peruvian Patent No. 17-2014/DIN is known in the state of the art which reports an explosive emulsion only for cold climates up to −40° C. comprising: a) aqueous oxidizing solution of inorganic salts comprising, by weight: from 60% to 85% of technical grade ammonium nitrate or fertilizer, from 4% to 18% of technical grade calcium nitrate, from 0.1% to 2% of thiourea and 8% to 15% water; b) continuous combustible phase formed by organic compounds of mineral, animal or vegetable origin of a liquid or solid nature including an agent or a mixture of surfactant agents of ionic and/or polymeric nature comprising, by weight, from 5% to 30% of emulsifier of an ionic nature, from 5% to 30% of emulsifier of a polymeric nature, from 4% to 40% of mineral, vegetable or animal oil, from 10% to 40% of microcrystalline wax, and from 15% to 50% of paraffin; wherein the emulsion sensitized with 1% to 5% by weight of glass microsphere bodies mixed with granular aluminum, and the gasifying agent comprises a solution of oxidizing salt of sodium nitrite having a pH of 5 to 7. Further, it refers to a process for producing the explosive emulsion.
On the other hand, the invention U.S. Pat. No. 4,456,492 is directed to an explosive compound in molten state comprising as the first component a molten mass that can be poured, pumped or flowed at a temperature in the range of −10° C. to +90° C. and comprising at least one oxygen-releasing salt, for example, ammonium nitrate, and at least one mass-soluble combustible material, e.g. urea, and as a second component pre-treated with ammonium nitrate. The explosive compositions show good detonation sensitivity retention under applied static pressure conditions, for example, in deep explosive wells. This composition discloses the use of ammonium nitrate, ammonium nitrate (prills), sodium nitrate, urea, thiourea, water, surfactants and combustibles such as paraffins, waxes, naphthas, among others. Further, it comprises the use of microspheres or microballs. Additionally, it mentions that such explosive compositions can also be used as fillers for explosive cartridges and, therefore, can be used as packaged explosives. However, this prior art teaches that the compositions should have additives for improving detonation sensitization such as formaldehyde condensates and naphthalenesulfonic acids of 1 to 10 carbon atoms, which counteract the possible loss of sensitization of the mixture, but should be used a little because of the high prices of this input.
The technical problems identified in the application in underground and/or open pit mining that are solved with the explosive mixture of greater energy, greater volume of gases, operation in cartridge diameter of ⅞″ (2.22 cm), stability at least 6 months and sensitivity to No. 8 detonator of the embodiments of the present invention are:
a) Decrease in life spam.
b) Insensitivity to No 8 detonator.
c) Not working on ⅞″ (2.22) diameter cartridges (critical diameter).
d) Difficulty of priming by hardening of the cartridges by crystallization of the explosive mixture.
e) Reduction of its explosive properties.
In this regard, the above-mentioned technical problems were overcome with the matrix emulsion of the embodiments of the present invention, which is formed by an oxidizing substance and a combustible substance, wherein the oxidizing solution for the embodiments of the present invention contain ammonium nitrate between 55% at 80% by weight as the largest component, sodium nitrate from 0.1% to 16% by weight, thiourea from 0.1% to 3.5% by weight as promoter of the gasification process and water from 6% to 18% % by weight.